1. Field of the Invention
The present invention relates to a zoom lens suitable for image pickup apparatuses provided with a solid image sensor such as video camera, digital still cameras, broadcasting cameras and monitoring cameras and for film cameras using a silver-halide film.
2. Description of the Related Art
Zoom lenses to be used for the above-mentioned image pickup apparatuses are required to have high optical performance. As one of the zoom lenses, a positive-lead type zoom lens whose most-object side lens group has a positive refractive power is known.
It is important for such a positive-lead type zoom lens, in order to achieve a wide angle of view, a high zoom ratio and high optical performance in its entire zoom range, to appropriately set its lens configuration (zoom type) and a configuration of each of lens groups constituting the zoom lens.
In general, in order to achieve high optical performance, it is necessary that various aberrations, particularly field curvature and astigmatism, be well corrected. For example, in order to achieve high optical performance in the entire zoom range with a high zoom ratio in the positive-lead type zoom lens, it is important to appropriately set lens groups to be moved during zooming and conditions relating to the movement of these lens groups.
Japanese Patent Laid-Open No. 01-126614 discloses a zoom lens including, in order from an object side to an image side, a first lens group having a positive refractive power, second, third and fourth lens groups to be moved during zooming and a fifth lens group having a positive refractive power and being not moved during the zooming, and further including an aperture stop placed between the fourth and fifth lens groups. This zoom lens moves during the zooming only the second, third and fourth lens groups placed further on the object side than the aperture stop, so that field curvature and astigmatism are significantly varied during the zooming, which makes difficult to correct them.
Japanese Patent Laid-Open No. 06-194574 discloses a zoom lens including, in order from an object side to an image side, first, second, third, fourth and fifth lens groups respectively having positive, negative, negative, positive and positive refractive powers, and moving these first to fifth lens groups during zooming. This zoom lens increases number of lens groups moved during the zooming in order to achieve a wide angle of view and a high zoom ratio. However, also in this zoom lens, the field curvature and the astigmatism are significantly varied during the zooming, which makes difficult to correct them.